Delayed coking process



United States Patent 3,338,817 DELAYED COKIN G PROCESS Fred S. Zrinscak, Woodhury Heights, and Grady L.

Payne, Mickelton, NJ., assignors to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Mar. 2, 1965, Ser. No. 436,686 2 Claims. (Cl. 208-46) The present invention relates to coke compositions and to a process for making the same. More particularly, the present invention relates to a process for making coke compositions capable of producing high density graphite and to the coke composition so produced.

At the present time, his desirable to produce high density graphite having generally uniform low porosity. Such graphite has excellent machinability qualities in that intricate shapes having close tolerances can be produced therefrom without high scrap losses. when the density of graphite is increased, compression strength, tensile strength, and oxidation resistance are increased proportionately. High density graphite having these characteristics can. be employed to produce excellent furnace linings and heavy duty electrodes.

Since graphite is produced from coke, it is desirable that the coke starting material be of a particular high quality in order for it to be capable of producing high density graphite; that is, the starting coke material should contain particular amounts of volatile combustible hydrocarbon material and a certain amount of benzene-soluble material. Up to the time of the present invention, the available cokes have not been capable of producing graphite having a high density by normal graphitizing methods.

It is an object of the present invention to provide a process for making coke compositions.

It is a further object of the present invention to provide coke compositions which can be employed to produce high quality graphite.

Further objects of the present invention will become evident from the following detailed description.

The present invention provides for a coke composition which contains condensed polynuclear aromatic hydrocarbon compounds, a portion of which is volatile. The polynuclear aromatic compounds are high molecular weight, highly unsaturated hydrocarbons, and are present in the coke compositions of the present invention in amounts such that the volatile combustible material is present in the range of from about 5 percent by weight to about 20 percent by weight, and preferably in the range of from about 11' to about 17 percent by weight, based upon the weight of the final coke composition. A portion of the polynuclear aromatic compounds in the coke composition is benzene-soluble and can be present in amounts in the range of from about 0.5 percent by weight to about 20 percent by weight, and preferably from about 4 percent by weight to about 17 percent by weight, based upon the weight of the final coke composition.

Coke compositions containing less than about 5 percent by weight total volatile hydrocarbon combustible material and less than about 0.5 percent by weight benzene-soluble material have been found to produce graphite of unsatisfactorily low density when made by normal graphitizing methods. On the other hand, coke compositions containing more than about 20 percent by weight volatile combustible material produce excess vapors during a graphitizing process and result in fractures in the graphite material.

It has. been found that coke compositions described above are capable of being formed into graphite having an apparent density above about 1.60 grams per cubic centimeter, and usually above about 1.70 grams per cubic centimeter by normal graphitizing methods. Specific examples of polynuclear aromatic materials having high amounts of volatile combustible materials which can be present in the coke compositions of the present invention include the hydrocarbons produced by pyrolysis of gas oils or naphtha or by thermal cracking or heat soaking of catalytic gas oil, heavy coker gas oil, furfural or phenol extracts of petroleum hydrocarbons or coal tar pitches.

The term soft point as used herein refers to the temperature at which a disk of the sample held within a horizontal ring is forced downward a distance of one inch under the weight of a steel ball as the sample is heated at a prescribed rate in a water or glycerine bath. This method for testing for soft point is described in ASTM- D-36-62T. The amount of volatile combustible material in the composition of the present invention is determined by the test described in ASTMD271. The amount of benzene-soluble material in the composition of the present invention is determined by the Barrett Test Method B7 described in the publication Methods of Testing Coal Tar Products copyright 1950 by Allied Chemical and Dye Corporation.

Apparent density as employed herein is intended to define the density of the graphite, including the voids therein. Apparent density is distinguished from real or true density in that the latter is the density of the graphite without the voids therein.

According to the process of the present invention, a high boiling hydrocarbon charge, such as virgin crude, bottoms from the vacuum distillation of reduced crude, thermal tar, Duo-Sol extract, furfural extract, vacuum tar, reduced crude, topped crude, and blends thereof, is first preheated to a temperature in the range of from about 850 F. to about 950 F. The preheated charge is then fed into the bottom portion of the coker drum, wherein it is subjected to a temperature in the range of from about 840 F. to about 930 F., with a coker outlet temperature in the range of from about 800 F. to about 870 F. The pressure in the coker drum is maintained at between about 10 and p.s.i.g. At these coker drum conditions, destructive distillation of the charge occurs and results in the formation of lighter boiling hydrocarbons and coke. The lighter boiling hydrocarbons are withdrawn from the coker drum, while the coke is caused to remain therein. As the high boiling hydrocarbon is continuously fed to the coker drum, the coke formed accumulates therein. When the desired amount of coke is formed, the preheated high boiling hydrocarbon feed thereto is discontinued.

Since the coke in the coker drum is continuously being accumulated, the coke which is first formed is subjected to the coker drum temperature for a longer period of time than is the later formed coke. It has been found that the first formed coke located in the bottom portion of the coker drum contains less volatile combustible material than the later formed coke located in the top portion of the coker drum. The amount of volatile combustible material present in the coke at a particular height in the coker drum is also dependent upon the coker reaction temperature employed. The amount of polynuclear volatile combustible material in the coke decreases as the reaction temperature in the coker drum is increased. Thus the amount of polynuclear volatile combustible material in the coke at a particular height is dependent on both the coker drum reaction temperature and the time the material therein is subjected to that temperature. By regulating the time of residence of the coke in the coker drum and the temperature to which it is subjected during that residence time, it is'possible to determine the height in the coker drum where the desired coke compositions will exist. For purposes of the present invention,

the desired coke compositions are present at a coker drum height where a temperature in the range of from about 800 F. to about 880 F. is maintained for about 0.5 hour to about 6 hours. However, the reaction time and temperature can be varied considerably within the above described ranges in order to obtain coke compositions having the amounts of volatile combustible materials and benzene-soluble materials within the above-described ranges. The feed to the coker drum is discontinued, when the desired amount of coke has been produced. After the coker drum feed is discontinued, the coke having the desired amount of polynuclear aromatic material therein is separated from the other coke and removed The desired coke composition can be separated by drilling a hole through the entire vertical length of the formed coke. 'T he coke at the top of the coker is cut off and allowed to fall through the hole and is removed. The desired coke located at an intermediary height is cut, allowed to fall through the hole, and is collected for further processing as desired.

In accordance with a more particular aspect of the process of the present invention, a high boiling hydrocarbon charge having an API gravity number in the range of from about to about 20, boiling predominantly above about 650 F., and preferably above 800 to 850 F., as for example topped crude, reduced crude, vacuum tar, and the like, is first preheated to a temperature of from about 850 F. to about 950 F. The preheated charge is then fed to the bottom portion of a coker drum and subjected therein to a temperature in the range of from about 840 F. to about 930 F. At these drum temperatures, a portion of the charge will be destructively distilled to produce coke and lighter boiling hydrocarbons. The lighter boiling hydrocarbons are withdrawn from the drum, with the lighter boiling hydrocarbons being processed as desired, while a portion thereof can be recycled to the bottom portion of the coker drum in admixture with the coker charge. The fraction which is recycled to admix with the coker feed has an initial boiling point above about 650 F. As the charge is fed continuously to the coker drum, the amount of coke continuously builds up therein. The coke produced in the first instance is located at the bottom portion of the drum, and, since it is subjected to high temperatures for a longer period of time than the later formed coke, the amount of polynuclear aromatic material is low compared to the later formed coke. The later formed coke in the upper portion of the drum contains the desired volatile combustible materials in total amounts in the range of from about 8 percent to about 20 percent by weight and benzene-soluble material in amounts in the range of from about 4 percent by weight to about 20 percent by weight. The coke having the desired amount of volatile combustible materials is that located near the top of the coker drum and is subjected to temperatures in the range of from about 820 F. to about 870 F. for a period of time of from about 0.5 hour to about 2.5 hours. The desired coke is then withdrawn from the coker drum at the particular range of height where it is stratified, and can be employed to produce graphite having an apparent density above about 1.60 grams per cubic centimeter, and usually above about 1.70 grams per cubic centimeter by normal graphitizing methods.

In accordance with another embodiment of the process of the present invention, a high boiling hydrocarbon charge having an API gravity in the range of from about 5 to about 20, as for example topped crude, reduced crude, vacuum tar, and the like, is first preheated to a temperature of from about 850 F. to about 950 F. The preheated charge is then fed to the bottom portion of a coker drum and subjected therein to a temperature in the range of from about 840 F. to about 930 F. The coke produced in the coker drum is continuously built up, and, as explained hereinabove, the composition of the coke will vary according to its height in the drum. It has been found that coke compositions containing from about 5 percent by weight to about 11 percent by weight of total volatile combustible material and between 0.5 percent and 4 percent by weight benzene-soluble material, though not capable of producing the desired graphite by normal graphitizing methods, can be improved in quality by the addition of certain materials rich in condensed polynuclear aromatic compounds after it is removed from the coker drum in order to produce high density graphite. This coke is produced after the charge is subjected to a temperature of from about 820 F. to about 880 F. for from about 1.2 hours to about 7 hours in the coker drum. The coke having the above compositions from the height in the coke drum where it is stratified. This coke composition can then be upgraded by the addition of materials having condensed polynuclear aromatic compounds therein and having a soft point in the range of from about F. to about 350 F., and preferably from about F. to about 270 F., and having a carbon to hydrogen atomic ratio in excess of about 0.90, and preferably in excess of about 1.0. The polynuclear aromatic compounds are added in amounts sufficient to bring the total volatile combustible material content up to about a range of 12 to 18 percent by weight and the benzenesoluble material content up to above about 4 percent by weight, based upon the weight of the final coke composition. Specific examples of additive materials are thermal asphalt having a soft point of F. to 265 F, produced by thermally cracking catalytic gas oil, furfural extract, pitch, binder pitch, petroleum binder pitch, coal tar binder pitch, and 245 F. soft point pitch from tars recovered in pyrolysis of gas oils to ethylene. The polynuclear aromatic material can be added to the coke composition in any convenient method, as for example crushing the coke and additive separately and later drymixing at elevated temperatures, or heating the tWo materials separately and later intimately mixing the two components in the heated conditions. Convenient temperatures which can be employed in order to ensure intimate mixing of the two components without causing a large amount of volatile evaporation are in the range of from about 120 F. to about 600 F., and preferably at a temperature about 50 F. to 100 F. higher than the soft point of the added polynuclear aromatic material. It has been found that the coke compositions produced from the above methods are capable of producing graphite having an apparent density above about 1.60 grams per cubic centimeter, and usually above about 1.70 grams per cubic centimeter, by normal graphitizing methods.

In the process of the present invention, it has been found that the amount of high quality coke produced can be increased by the addition of certain cracked aromatic hydrocarbon components to the coker charge. This addition results in an increase of polynuclear high volatile content material in the coke at a given coker drum temperature and coke residence time. The cracked hydrocarbon components which can be added are those which boil in the range of from about 650 F. to about 1100 F. and include coker heavy blowdown liquid, thermally cracked tar, syn tower bottoms, and the like. These cracked materials can be added to the charge by recycling the cracked materials boiled off the coker drum back to the drum or from an outside source. In addition, these materials can be formed in the charge by increasing the residence time at high temperatures in the preheating step. The cracked materials enumerated above are added to the hydrocarbon coker feed in amounts of above about 1 percent by weight of the hydrocarbon coker feed. These cracked materials can also form 100% of the coker feed.

The following examples are intended to enable a fuller understanding of the present invention and are not to be interpreted as limiting the same.

In all the examples shown below, the coke com-positrons were graphitized by normal graphitizing methods. The coke was first ground and then mixed with a binder. The resultant mixture was then pressure-molded into the shape desired and thereafter the molded coke was removed from the mold and packed in finely ground coke under pressure. The packed, molded shape was heated to a temperature of about 1000 C. and then brought up to a temperature of from about 2500 C. to about 3000 C. The heating from 1000 C. to 2500 C. was done slowly and took about 12 hours. The resultant molded graphite was then allowed to cool.

EXAMPLE 1 A mixture of virgin reduced crude, boiling in the range predominately above 800 F., and about 7 percent by weight of catalytic heavy gas oil, boiling predominately above 800 F.; the mixture having an API gravity of about 15, was preheated to a temperature of about 920 F. The charge was then continuously introduced into a coker drum having a weight of about 62 feet for about 16 hours. The coker outlet temperature was 840 F. A portion of the high boiling cracked vapors withdrawn from the coker was recycled to mix with the feed in an amount in the range of from about 25 to about 30 percent by weight of the reduced crude. After about 16 hours, the coke had built up into the coker to about 40 feet. Two coke samples were withdrawn from the coker; the first sample being withdrawn from a height of from the top level of coke to 10 feet below the top level of coke, which had been in the drum for an average of two hours, and the second being withdrawn from the bottom 10 feet of the drum, which had been in the drum for an average of about 14 hours. The first sample contained about 11.7 weight percent of volatile combustible material. The amount of benzene-soluble material was about 4.5 percent by weight, based upon the weight of the coke composition. The graphite produced therefrom had an apparent density of 1.79 grams per cubic centimeter. The second sample contained about 7.5 percent by weight volatile combustible material. The amount of benzene-soluble material was less than 0.5 percent by weight, based upon the weight of the coke composition. The graphite produced therefrom had an apparent density of 1.00 gram per cubic centimeter. The graphite having a density of 1.79 grams per cubic centimeter had a compression strength in the range of 17,000 to 18,000 p.s.i., a tensile strength of about 10,000 p.s.i., and an electrical resistivity of about 0.002 ohm per centimeter. The oxidation resistance of this graphite was also greatly improved over the presently available graphite.

EXAMPLE 2 This example shows the effect of the addition of cracked components to the coker charge. In each of the following runs, a reduced crude having an API gravity of about 17 API and boiling predominately above 800 F. was preheated to a temperature of about 930 F. The preheated reduced crude was charged to a coker drum at the rate of about 6900 barrels per day for about 16 hours. In each run, the charge in the coker was subjected to a temperature of from about 860 F. to about 910 F. The following table shows the effect of adding heavy coker blowdown oil to the coker charge.

Graphite Apparent Density,

gm./cc.

Percent Wt. of Blowdown Oil to Charge Depth in Drum Run of Coke-Ft.

. EXAMPLE 3 This example shows the effect on graphite density of adding materials consisting essentially of condensed polynuclear aromatic compounds to coke which is employed in the production of graphite. The coke in this example was prepared by first preheating a reduced crude having an API gravity of about 17 API and boiling predominately above 800 F. to a temperature of about 930 F. The preheated reduced crude was continuously charged at a rate of about 6500 barrels per day to a bottom portion of a coker drum and subjected to a temperature of from about 860 F. to about 900 F. wherein the charge is coked. The heavy portion of the coker vapors were fractionated and recycled to the coker charge at a recycle ratio of about 0.16 to 1. The coking was continued for about 16 hours, whereupon the amount of coke residing in the drum had reached a height of about 40 feet. Three samples of coke were removed from the coker drum at a level of 5 feet from the top which had been in the drum for an average of about 2.5 hours. Each sample contained about 9.3 wt. percent of volatile combustible material and about 1.0 wt. percent of benzene-soluble material. Three samples were made from the product. One sample was not mixed with a condensed polynuclear aromatic material, while the two remaining samples were mixed each with a separate condensed aromatic material prepared from thermally cracked catalytic gas oil, which materials have the physical characteristics shown in the following table:

The condensed aromatic materials shown in the above table were added to the coke samples, as shown below, and the graphite produced therefrom by normal graphitizing methods had the apparent densities shown below:

Total, Percent Wt. Wt. Graphite Wt. Wt. Percent Percent Apparent Sample Percent Benzene F. 265 F. Density,

Combusti- Soluble Asphalt Asphalt gm./cc.

bles Material The asphalts were added to the coke samples by first crushing the two components to a size small enough to pass through one-quarter inch mesh. The two materials were dry mixed and then subjected to -a temperature of about 300 F. in an oven for one hour. During the heating, a portion of the volatile material was vaporized from the mixture. After being heated, the mixture was removed from the oven, allowed to cool, and then recrushed. The mixture was then graphitized.

As can be seen from this example, coke compositions which do not initially contain a sufiicient amount of volatile combustible material or benzene-soluble material to produce high density graphite can be upgraded by the addition of certain materials to produce graphite having a satisfactorily high density.

Having fully described the invention, we claim:

1. The process for making a coke composition capable of producing high density graphite, which comprises preheating a high boiling petroleum hydrocarbon to a temperature of from 850 F. to 950 F., heating the preheated hydrocarbon in a coker to a temperature of from 840 F. to 930 F. to produce coke and a hydrocarbon coker efiluent and separating out the coke having volatile combustible material in total amounts ranging from about 8 percent to about 20 percent by weight and benzenesoluble material in amounts ranging from about 4 percent to about 20 percent by weight which has been subjected to a coker temperature of from 820 F. to 870 F. for from 0.5 to 2.5 hours.

2. The process for making a coke composition capable of producing high density graphite, which comprises feeding to a coker a mixture of high boiling petroleum hydrocarbon and above 1 weight percent by weight, based upon the Weight of said mixture, of an aromatic hydrocarbon preheated to a temperature of from 850 F.,to 950 F., heating the hydrocarbon mixture in the coker to a temperature of from 840 F. to 930 F. to produce coke and a hydrocarbon coker efiluent, fractionating the hydrocarbon coker efiluent and recycling a hydrocarbon coker effluent fraction boiling above 800 F. to admix with the high boiling hydrocarbon coker feed, and separating out the coke having volatile combustible materials in total amounts ranging from about 8 percent to about 20 percent by Weight and benzene-soluble material in amounts ranging from about 4 percent to about 20 percent by weight which has been subjected to a coker temperature of from 820 F. to 870 F. for from 0.5 to 2.5 hours.

References Cited UNITED STATES PATENTS 2,775,549 12/1956 Shea 20s 52 2,922,755 1/1960 Hackley 208-106 3,035,989 5/1962 Mitchell 201-17 3,173,852 3/1965 Smith 208-106 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,338 ,817 August 29 1967 Fred S. Zrinscak et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 18, for "when" read When column 4, line 11, after "compositions" insert is removed column 5, line 16, for "weight" read height line 74, for "greater" read great Signed and sealed this 22nd day of October 1968.

(SEAL) Attest:

EDWARD J BRENNER Edward M. Fletcher, 11'.

Commissioner of Patents Attesting Officer 

1. THE PROCESS FOR MAKING A COKE COMPOSITION CAPABLE OF PRODUCING HIGH DENSITY GRAPHITE, WHICH COMPRISES PREHEATING A HIGH BOILING PETROLEUM HYDROCARBON TO A TEMPPERATURE OF FROM 850*F. TO 950*F., HEATING THE PREHEATED HYDROCARBON IN A COKER TO A TEMPERATURE OF FROM 840*F. TO 930*F. TO PRODUCE COKE AND A HYDROCARBON COKER EFFLUENT AND SEPARATING OUT THE COKE HAVING VOLATILE COMBUSTIBLE MATERIAL IN TOTAL AMOUNTS RANGING FROM ABOUT 8 PERCENT TO ABOUT 20 PERCENT BY WEIGHT AND BENZENESOLUBLE MATERIAL IN AMOUNTS RANGING FROM ABOUT 4 PERCENT TO ABOUT 20 PERCENT BY WEIGHT WHICH HAS BEEN SUBJECTED TO A COKER TEMPERATURE OF FROM 820F. TO 870*F. FOR FROM 0.5 TO 2.5 HOURS. 